This invention relates to an image recording apparatus, and in particular, to an image recording apparatus using photo-setting ink.
In recent years, in comparison with a method requiring plate making, such as a photogravure printing method or a flexographic printing method, an image recording apparatus based on an ink jet printing method has come to be used in a large number of cases for the reason that an image can be recorded simply at a low price.
Further, in a field where an image recording process is applied to a commodity or a package of a commodity by means of an image recording apparatus based on such an ink jet method, a material having no ink absorbing property, such as resin or metal, is used for a commodity or a package of a commodity in many cases. Further, it is known that in an image recording apparatus which uses a material having no ink absorption ability for a recording medium, photo-setting ink is fixed to the recording medium, after being hardened and fixed by the radiation of light, such as ultraviolet rays (for example, the publication of the unexamined patent application 2002-347232).
This image recording apparatus is equipped with a conveyance unit for conveying a recording medium, and over the conveyance path of a recording medium by means of this conveyance unit, a plurality of line type printing heads for jetting photo-setting ink drops are arranged along the conveyance direction. Further, at the downstream side of these printing heads with respect to the conveyance direction, a light radiation device for radiating light to ink drops jetted from the printing heads to harden the ink drops is disposed.
In such an image recording apparatus, it is actualized that, while a recording medium is being conveyed by the conveyance unit, ink drops are being jetted from the printing heads to the recording medium in accordance with specified image information, and after that, by the radiation of light emitted from the light radiation device to the ink drops landed on the recording surface, the ink drops are hardened and fixed on the recording medium.
Further, up to this time, in an image recording apparatus, it has been put into practice that a constant quantity of light is uniformly radiated to the ink drops which have been jetted from the printing heads and landed on a recording medium by the light radiation device to harden the ink drops completely.
However, supposing in the above-mentioned image recording apparatus, the distance to the light radiation device becomes different for each printing head. Owing to this, the time from the landing to the radiation by the light emitted by the light radiation device becomes different for each printing head, which makes the dot diameters after setting have a dispersion. On top of it, there is a possibility that dots of their respective colors after landing are mixed with one another before they reach the light radiation device, which has been the cause of the degradation of color reproducibility.
Further, in recent years, in the same manner as other electronic equipment, it is desired to make the image recording apparatus smaller-sized. However, if the distance between the printing heads and the light radiation device is made smaller, ink mist becomes easy to adhere to the light radiation device. If a large amount of ink mist adheres to the light radiation device, the quantity of light is lowered and becomes incapable of hardening ink drops on a recording medium with certainty. In particular, in the case where a plurality of light radiation devices are provided for the plurality of printing heads respectively, even if one light radiation device is subjected to the lowering of quantity of light, the quantity of light required for the hardening reaction cannot be secured, which becomes the cause of image quality degradation.